When I start our 59 Desoto after it sits for a few days the engine will speed up as the brake is depressed.This stops after a few seconds .There just does not feel much power assist to the brakes when driving.The booster is a Bendix can type. Any thoughts? Thanks ahead .

pinch off the hose to the booster and then try the brakes. My 57 Desoto would have a change in idle when using the brakes. It would actually slow down though. Booster Dewey rebuilt the booster and the problem was solved.